1. Field of the Invention
The present invention relates to resin molded objects such as, for example, resin windows that can be used, for example, as a sunroof of a car, as well as methods and dies used for manufacturing such resin molded objects.
2. Description of the Related Art
Window units made of transparent resin materials that are lighter than glass have been used as sunroofs and other windows in various types of vehicles in order to replace similar glass units that are designed to allow light into the inside of the vehicle. Resin materials have been substituted for glass materials because functionally similar units are much lighter in weight and thereby allow the manufacturer to reduce the overall weight of the vehicle. Such resin windows typically have been manufactured using injection-molding techniques, and typically transparent synthesized resins, such as polycarbonate or acrylic resins, have been utilized.
However, known resin-molded windows have been subject to problems because the resin material does not provide sufficient rigidity against bending and twisting. Reduced rigidity in comparison to similar glass window units results because the elastic modulus of resin is lower than that of glass.
One known technique for overcoming this rigidity problem is to provide an integrally formed reinforcing rib 12 around the periphery of the window body on the inside surface of the window unit, as shown in FIGS. 21 and 22. When such a reinforcing rib 12 is formed, however, sink marks are known to appear on the surface of the window body 11 corresponding to the rib-formed portion, as a result of the injection molding manufacturing process used to fabricate such resin window units. Thus, when reinforcing the resin window unit to increase rigidity, another problem, namely the external appearance of the window is spoiled, is created. Consequently, when the total size of the window is large and/or when the external appearance of the window is a matter of great importance, such resin-molded objects can not be reinforced with such a rib 12.
In addition, known resin window units have been designed with a reinforcing member 13 made of steel, aluminum, or the like. In such a case, the reinforcing member 13 effectively reinforces the window in conjunction with the rib 12. However, this design increases the weight of the resin window unit and minimizes the reduced weight advantage that resin window units have over glass window units.